Professor Bainbridge in the course of an interesting discussion of VE Day and the strategic bombings of German and Japaniese civilian populations notes:

Indeed, there seems little doubt but that the strategic bombing campaign violated the precepts of a just war. In particular, it violated the tenets of proportionality and discrimination. Proportionality holds that the response to aggression should not be disproportionate to the original aggression. Was the deliberate firebombing of Dresden or Hamburg, say, proportional to the Blitz? As for discrimination, there is no doubt that Bomber Harris and his US counterparts deliberately targeted German and Japanese citizens.

So, at point do the Afghani and Iraqi campaigns breach the proportionality principle? When we have killed 3000 of them? Destroyed property in value equal to the WTC buildings and related economic damage? Or, what?